Transcript If we could see atoms

If we could see atoms,
kids might …
Lynn A. Melton
University of Texas at Dallas
[email protected]
Mini-CAST January 26, 2008
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Sequence of Ideas
Comments on Teaching*
Fundamental Concepts of Chemistry*
Chemistry Seems Arcane*
Models
Definition of Atom*
Data for atoms
Atomic Force Microscopy (AFM)
Mass Spectroscopy (MS)
Hands On
Atoms* (Seeing Without Seeing)
AFM
MS
* = today
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Comments on Sequence
• Lots of ideas there
• It you use this material in the classroom, it
may take you a month or more to work
through the material.
• The “hands on” stuff will count as labs.
• No algebra! No exponents!
3
Comments on Teaching
• What can the Coca-Cola Company tell us
about teaching?
– Advertisements are delivered to a passive
audience.
4
Comments on Teaching
• What can the Coca-Cola Company tell us
about teaching?
– Advertisements are delivered to a passive
audience.
– “It takes 20 reps of an ad to start to move the
market.”
5
Comments on Teaching
• What can the Coca-Cola Company tell us
about teaching?
– Advertisements are delivered to a passive
audience.
– “It takes 20 reps of an ad to start to move the
market.”
– “It takes 8 reps for the audience to know that
the ad is running.”
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Comments on Teaching
• What can the Coca-Cola Company tell us
about teaching?
– Concepts are delivered to a passive audience.
– “It takes 20 reps of a concept to start to move
the minds.” ??
– “It takes 8 reps for the students to know that the
concept is there.” ??
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Fundamental Concepts of
Chemistry
• Atoms
• Bonding/Molecules/Reactions
• Structure/Properties
– Activity of molecule derives from its structure
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Chemistry Seems Arcane
A conceptual chemistry problem:
• Question: Does the blackened copper wire
weigh more, same, or less than when it was
in the flame?”
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Chemistry Seems Arcane
• A secondary school teacher was in the class,
and came to me for help with this
homework problem.
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Chemistry Seems Arcane
• She could tell me that the flame cleaned the
surface of the dirty copper wire and that
oxygen from the air reacted with the clean
surface to produce copper oxide, which is
black.
• She went back and forth as to whether the
weight was “more”, “same”, or “less”.
• She was guessing.
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Chemistry Seems Arcane
• I tried to help. Knowing that she once had
taught Home Economics, I said, “Go to the
grocery store and fill a basket with oranges.
Now put a layer of avocados on top of the
oranges. Does the basket weigh more, same
or less when I add the avocados?
• “Oh, Dr. Melton, of course it weighs more”.
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Chemistry Seems Arcane
• She could reason well enough, but when she
was asked about atoms, she turned off her
reasoning. The atomic world seemed
ARCANE.
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Chemistry Seems Arcane
• The atomic world seemed ARCANE.
– Known or understood by only a few: arcane
economic theories.
– adj : requiring secret or mysterious knowledge;
"the arcane science of dowsing“
– Definitions from dictionary.com
• In the arcane world, the normal rules do not
work, and you might as well guess.
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Chemistry Seems Arcane
• Would she have guessed if she could have
seen atoms?
• Can your students see atoms?
• The atomic world seemed ARCANE.
– In the arcane world, the normal rules do not
work, and you might as well guess.
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Atoms: Key Question
• If a sassy eighth grader asked you “So why – other
than you and the book say so – should I accept
that the world is granular? After all, I cannot see
atoms.”
• Your answer has three parts:
– Define an atom carefully
– Data #1:Atomic Force Microscopy
(the world is granular)
– Data #2: Mass Spectrometry
(the particles have different weights)
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Atoms
• Definition of an atom (a la Melton)
– Rip any piece of the world apart, but you may
use only the energies available to the ancients –
horses, flames, and lightning. When you
cannot rip the smaller pieces apart any longer
[to produce only neutral particles] then those
last [neutral] particles are ATOMS.
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Atoms
Digression
• Words that may come up. (If they don’t ask, don’t
bring them up; Keep to the simple model)
– Electron, proton, neutron: subatomic particles, they will
be discussed as more complex MODELS
– Element: a group of atoms all of which have the same
number of protons
– Ion: a atom in which the number of electrons is not the
same as the number of protons
– Isotopes: atoms that have the same number of protons
but different numbers of neutrons
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Atoms: Getting the Concept
• The weight of anything in the world is the same,
regardless of how finely you divide it.
• Or, when you add up the weight of all the pieces,
you get the weight of the original thing.
• The world is granular; it is
– Sand rather than shampoo
– Grapes rather than jello
• Every material in the world is built from atoms.
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Let’s Work with Atoms
• This hands-on exercise is part of a series of
lessons, all designed to help students accept
that atoms are real.
• Since, atoms are too small for us to see with
our eyes, let’s work on Seeing Without
Seeing.
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Atoms
Seeing Without Seeing
• What do we need to know about atoms?
– What is your weight?
– What can I build with you? (or, What other
atoms can you bond to?)
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Atoms
Seeing Without Seeing
• Each team must have an A and a B
– A is the person with the gaudiest clothing
• In this exercise, A is the “doer” and B is the
“recorder”.
– A may not write
– B may not touch.
• We will switch roles later.
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Atoms
Seeing Without Seeing
• A space probe has just returned from Planet
Xanadu with samples of material.
• Your assignment is to go into the laboratory and
find out whether the samples display the same
chemistry that we observe on earth.
• In particular, on Planet Xanadu, is there a
periodic table?
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Atoms
Seeing Without Seeing
• The garbage bag is your laboratory. It
contains material from Planet Xanadu.
• One person inserts both hands into the
garbage bag and does the research. The
other person records the results.
• Please do not peek. At the right time, I will
tell you when to look.
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Atoms
Seeing Without Seeing
• Carry out your research, write up the results,
and make sure that A and B agree on what has
been written.
• Switch bags with adjacent team.
• Check the results of the other team, but now A
is the “recorder” and B is the “doer”.
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Atoms
Seeing Without Seeing
• Now, the whole group discusses their results.
• This is our version of an international scientific
meeting.
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Atoms
Seeing Without Seeing
• Hands On Time!
• Go to it!
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Atoms
Seeing Without Seeing
• Switch bags with another team.
• Each team analyzes the other sample.
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Atoms
Seeing Without Seeing
• Now, all together, let’s discuss the results.
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Atoms
Seeing Without Seeing
• On Planet Xanadu, is there a periodic table?
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Atoms
Seeing Without Seeing
• Now, look at the atoms.
• What do we see with our eyes?
• Why are the atoms made the way they are?
–
–
–
–
Color?
Shape?
Weight?
Bonding?
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Atoms
What data do we have?
• Atomic Force Microscopy
– A very sensitive probe is scanned across the
surface, and the force on the probe is measured
– By using electronics to keep the force constant,
we can – line by line – generate a profile of the
surface
– The best instruments can “feel” individual
atoms.
– Conclusion: the world is granular.
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Atoms
What data do we have?
•
•
•
•
•
Atomic Force Microscopy (neat websites)
http://www.mee-inc.com/afm.html
http://www.rhk-tech.com/hall/NaCl-mica.html
http://stm2.nrl.navy.mil/how-afm/how-afm.html
http://www.omicron.de/index2.html?/results/atomi
c_resolution_on_si_111_7x7_in_non_contact_mo
de_afm/~Omicron
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Atoms
What data do we have?
•
•
•
•
•
Atomic Force Microscopy (neat websites)
http://www.mee-inc.com/afm.html
http://www.rhk-tech.com/hall/NaCl-mica.html
http://stm2.nrl.navy.mil/how-afm/how-afm.html
http://www.omicron.de/index2.html?/results/atomi
c_resolution_on_si_111_7x7_in_non_contact_mo
de_afm/~Omicron
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Atoms
What AFM data do we have?
Silicon surface
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Atoms
What AFM data do we have?
NaCl (salt) surface
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Atoms
What AFM data do we have?
• Conclusion:
– The world “feels” granular.
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Atoms
What MS data do we have?
• Mass Spectrometry separates atoms
(actually ions) according to their differing
masses.
• Different masses have different trajectories!
• Real mass spectrometers require a very
good vacuum, and they are expensive.
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Atoms
What MS data do we have?
• Mass Spectrometry separates atoms (actually ions)
according to their differing masses.
• Neat websites!
• http://www.chem.arizona.edu/massspec/example_
html/examples.html
• http://www.cea.com/cai/simstheo/mspectra.htm
• http://www.chemguide.co.uk/analysis/masspec/ele
ments.html
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Atoms
What MS data do we have?
The different elements have different masses.
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Atoms
AFM and MS
• AFM – The AFM box allows students to
mimic the measurements made with a real
AFM. Maybe you can feel individual
atoms?
• MS – The mass spectrometer allows
students to mimic the measurements made
with a real mass spectrometer. Do you want
to see the trajectories of your atoms?
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Atoms
Making Stuff
• What does it cost?
• Atoms -- average cost is about $0.10 per
atom (steel costs $0.08 per atom)
• AFM -- $2-5 (most of the cost is velcro)
• MS -- $2
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Should I use this approach
in my class?
• It (probably) will help students with the
fundamental concepts of chemistry.
• Perhaps you are constrained by the
sequencing of chemistry instruction?
• Perhaps you are constrained by TEKS and
TAKS?
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Should I use this approach
in my class?
• Perhaps you are constrained by the
sequencing of chemistry instruction?
• 8th grade ???
[pre-AP chemistry  AP chemistry 
Freshman Chemistry  degree in chemistry]
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Should I use this approach
in my class?
• Perhaps you are
constrained by TEKS
and TAKS?
• “Which letter in this
model of a boron atom
represents a neutron?”
(TAKS grade 8 science
April 2006)
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What can we do together?
• Longer workshops on this theme?
– Get 10 teachers together and ask me
– Atoms (and how to make a set)? Density?
Gases and Pressure?
• Course at UTD “Lab and Demonstrations
for Middle School” -- Spring 2009
• Research/publication on the effectiveness of
this approach?
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If we could see atoms, kids might…
• Help me fill this in…
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Contact Info
Dr. Lynn Melton
Department of Science/Mathematics Education
UT-Dallas
800 W. Campbell Road
Richardson, TX 75080
[email protected]
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